Separation of CO2 and H2S Using Room-Temperature Ionic Liquid [bmim][MeSO4

Abstract

We have developed a ternary equation of state (EOS) model for the CO 2 /H 2 S/1-butyl-3-methylimidazolium methylsulfate ([bmim][MeSO 4 ]) system to understand separation of these gases using room-temperature ionic liquids (RTILs). The present model is based on a modified RK (Redlich-Kwong) EOS, with empirical interaction parameters for each binary system. The interaction parameters have been determined using our measured VLE (vapor-liquid equilibrium) data for H 2 S/[bmim][MeSO 4 ] and literature data for CO 2 / [bmim][MeSO 4 ] and CO 2 /H 2 S. Due to limited VLE data for H 2 S/[bmim][MCSO 4 ], we have also used VLLE (vapor—liquid—liquid equilibrium) measurements to construct the EOS model. The VLLE for H 2 S/ [bmim][MeSO 4 ] is highly asymmetric with a narrow (mole fraction H 2 S between 0.97 and 0.99) LLE gap which is the first such case reported in the literature and exhibits Type V phase behavior, according to the classification of van Konynenburg and Scott. The validity of the ternary EOS model has been checked by conducting VLE experiments for the CO 2 /H 2 S/[bmim][MeSO 4 ] system. With this EOS model, solubility (VLE) behavior has been calculated for various (T, P, and feed compositions) conditions. For large (9/1) and intermediate (1/1) CO 2 /H 2 S feed ratios, the CO 2 /H 2 S gas selectivity is high (10 to 13, compared with <4.5 in the absence of ionic liquid) and nearly independent of the amount of ionic liquid added. For small CO 2 /H 2 S mole ratios (1/9) at 298.15 K, increasing the ionic liquid concentration increases the CO 2 /H 2 S gas selectivity from about 7.4 to 12.4. For high temperature (313.15 K) and large CO 2 /H 2 S feed ratios, the addition of the ionic liquid provides the only means of separation because no VLE exists for the CO 2 /H 2 S binary system without the ionic liquid.